The invention relates to a fuel cell system in which anode exhaust gas is recirculated to the anode inlet.
This fuel cell system comprises an anode circuit having a gas jet pump with two inlets and one outlet, for conveying surplus hydrogen from the anode outlet to the anode inlet. A “motive jet” under elevated pressure is introduced at one inlet, and passes through the gas jet pump to its outlet. A further inlet of the gas jet pump is arranged such that the motive jet flowing through the gas jet pump produces a low pressure at the further inlet, and is thereby able to draw in gas via the further inlet and entrain it as far as the outlet.
It is known in particular from fuel cell systems to utilize the high pressure which hydrogen is conventionally under in a hydrogen tank to form a motive jet for a gas jet pump. The gas jet pump is thus arranged between the hydrogen tank and the anode inlet. As a result, the quantity of anode waste gas that is drawn in via the further inlet of the gas jet pump is directly dependent on the quantity of hydrogen gas supplied from the tank and forming the motive jet, which in turn depends on the fuel cell system load.
This known arrangement is problematic under low load. In particular, it would then be desirable for somewhat more anode waste gas to be recirculated than is possible with the gas jet pump. Satisfactory recirculation under low loads has heretofore been made possible, if need be, by using a blower. However, a blower is a complex and expensive component, which is susceptible to failure in particular at cold temperatures due to icing.
It is therefore an object of the present invention to provide a fuel cell system which operates reliably, even under low loads, and is nonetheless inexpensive.
This and other objects and advantages are achieved by the fuel cell system according to the invention, in which a part of the anode waste gas is supplied to a compressor, which comprises it and supplies it to the motive jet side of a gas jet pump. In this way it is ensured that a sufficient quantity of gas in particular a quantity sufficient for low loads, is always available on the motive jet side. In practice only very small quantities of anode waste gas need to be compressed, such that the power of the compressor may be so low that it can be operated with a 12 volt power supply. Expenditure is therefore low, while the solution is nevertheless effective.
It is advantageous, first of all, for hydrogen from a tank also to be supplied to the same gas jet pump to which the compressed waste gas is supplied, as in the prior art. This may be achieved by bringing the compressed waste gas and the hydrogen from the tank together upstream of the gas jet pump. It needs to be ensured that the compressed waste gas and the hydrogen are at roughly the same pressure. The compressed waste gas and the hydrogen may however also be supplied directly to the gas jet pump independently of one another, using different inlet nozzles.
Another embodiment of the invention has two gas jet pumps, to one of which the compressed waste is supplied, with hydrogen from the tank being supplied to the other. Each gas jet pump then has a part of the uncompressed waste gas supplied to it as gas to be drawn in. With this embodiment too it is ensured that the fuel cell system functions under low loads.
To prevent flow in undesired directions, all the gas jet pumps in this embodiment need to have a nonretum valve on the anode inlet side.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.